1. Field of the Invention
This invention relates to structure for absorbing forces resultant from shock and, in particular, to structure for absorbing forces from a non-operational shock inflicted upon a computer disk drive, i.e., a shock inflicted during storage or transport of the computer disk drive.
2. Related Art
In computer systems, information is frequently stored in a magnetic film on the surface of a hard or soft disk. The information is stored in concentric tracks in the magnetic film, and is written to or read from the film by means of a magnetic head (or "slider" or "transducer"). When storing or retrieving data, the magnetic head rides on a thin laminar boundary layer of air over the rapidly rotating disk, thereby avoiding direct contact of the head with the magnetic surface of the disk.
On most disk drives, the magnetic head is mounted near the end of a member commonly referred to as an actuator. Two configurations of actuators, linear and rotary, have been widely used. In the linear configuration, the actuator moves linearly along a radial line of the disk to position the magnetic head at a desired position above the magnetic surface of the disk. In the rotary configuration, the actuator rotates about a pivot point near the periphery of the disk, the magnetic head swinging so as to define an arc as the magnetic head is positioned above the magnetic surface of the disk.
Disk drives are further categorized by the position of the magnetic head when the drive is not operating. In a dynamic loading drive, the actuator on which the magnetic head is mounted is withdrawn to a position away from the disk (typically on a ramp) when the drive is not operating. In a contact start/stop drive the magnetic head rests at a "park" position on a non-data region of the surface of the disk (typically the inner portion thereof) when the drive is not operating.
Vibrations and shocks that may damage the disk drive can occur during operation of the disk drive ("operational" vibrations and shocks). Shocks can also occur while the disk drive is not operating ("non-operational" or "non-op" shocks), such as during storage or transport of the disk drive. Damage due to shock and/or vibration has become even more of a problem with the advent of "laptop" and "hand-held" computers, which are often used in severe environments and bumped or dropped repeatedly as they are moved from place to place.
Both dynamic loading and contact start/stop disk drives need to be protected against external vibration and shocks. In dynamic loading drives, the bearings of the spindle-motor are particularly vulnerable. A sizeable shock imposed on the drive can plastically deform or Brinell the races in these bearings. Such deformations in the bearing races may cause the disk to wobble in a lateral direction as it rotates (a condition referred to as "high runout") and may create tracking problems. Acoustic degradation caused by the clicking of the Brinelled bearings may also result. Moreover, Brinelling creates undue friction in the bearings and may slow down the rotation of the disk or prevent the disk from rotating altogether.
In contact start/stop drives, a shock on the drive may lead to "head slap", in which the head is lifted from and falls back to the surface of the disk. Such contact between the head and disk can damage the head and/or the disk surface.
Certain shocks produce large forces in a direction perpendicular to the disk, potentially causing sufficient displacement of the disk or other components of the disk drive so that the disk contacts one of the other components, resulting in damage to the disk. In previous disk drives, the clearance between the disk and the actuator has been maximized to prevent such contact. In previous disk drives including multiple disks having a disk-to-disk spacing of 3.00 mm, the spacing between each disk and the associated actuator has been limited to no more than 0.35 mm.
Newer, thinner disk drives using smaller magnetic heads (50% sliders) require smaller disk-to-actuator clearance. For example, a disk drive having a disk-to-disk spacing of less than 2.25 mm requires a clearance between the disk and actuator of less than 0.22 mm in order to package four magnetic heads and two disks in a type 3 form factor disk drive. Thus, in these smaller disk drives, a smaller displacement of the disk, as compared to older drives, can result in contact between the disk and other components of the disk drive. Additionally, the smaller pre-loads, e.g., 3.0 to 4.0 grams, used with 50% sliders are not adequate to hold the head gimbal assembly (i.e., magnetic head mounted on a suspension) of the actuator in the rest position for relatively large shocks, e.g., 150 g's of acceleration, so that the head gimbal assembly is lifted up and then falls, resulting in contact of the head gimbal assembly with the disk.
Further, the baseplate thickness in many newer drives has been reduced. The disk drive spin motor is attached to the baseplate and one or more disks are attached to the spin motor. The thinner baseplate allows increased displacement of the high mass spin motor, resulting in increased displacement of the attached disk or disks and greater danger of contact with other disk drive components. Additionally, the disks of the disk drive can also deflect, resulting in contact between the disks and a disk drive component.
In one attempt to alleviate these problems, disk drives have been mounted with elastomeric grommets and screws or with isolators having studs attached to the ends. Both of these methods have disadvantages. First, grommets or isolators take up significant space, and space is at a premium in a small computer. Second, these methods involve several parts which must be assembled and installed. The extra expense arising from these steps can be substantial in the context of mounting a relatively small component such as a disk drive in a laptop, hand-held or other miniature computer.